1. Field of the Invention
The present invention relates to an extruder for rubbery materials, which is capable of exchanging die plates at a high speed.
2. Description of the Related Art
Various types of extruders for extruding rubbery materials are known. For example, JP-B-4-42,175 discloses an extruder which comprises an extruding unit having a die holder with a horizontal lead-through groove. A die plate is slidably arranged in the lead-through groove of the die holder, for forming a strip rubber member with a predetermined cross-section by extruding a rubbery material through the die plate in a direction perpendicular to the lead-through groove. A cylinder device is associated with the extruding unit, and has a piston rod with the tip end detachably connected to the die plate. In this instance, when it is necessary to form a strip rubber member with a different cross-section by using the same extruding unit, the current die plate has to be changed with a next die plate. To this end, the piston rod of the cylinder device is moved backward to pull the current die plate out of the lead-through groove, and the piston rod is then moved forward to set a next die plate and push it up to the extruding position of the lead-through groove.
Such an arrangement of the known extruder suffers from a problem that, when the current die plate is pulled out of the lead-through groove and removed from the piston rod and replaced by a next die plate, the operator has to perform manual operations for changing the die plates because the extruder is not equipped with a unit for these operations.
A similar extruder for rubbery materials is also disclosed in JP-A-57-210,839, which includes an extruding unit having an extruding head formed with a horizontal lead-through groove, a die holder slidably arranged in the lead-through groove of the extruding head, and two die plates which are removably arranged on the die holder, i.e., a current die plate and a next die plate. The die holder is moved by a cylinder device along the lead-through groove. A strip rubber member with a predetermined cross-section is formed by extruding a rubbery material through the current die plate in the direction perpendicular to the lead-through groove. In this instance, the die plates are changed by operating the cylinder device to move the die holder along the lead-through groove so that the current die plate is ejected at the lateral side of the die holder (the current die plate becomes the last die plate after it has been ejected), moving the next die plate until it reaches an extruding position (the next die plate becomes the current die plate after it has reached the extruding position), and thereafter replacing the last die plate ejected to the lateral side of the die holder with the next die plate.
This type of extruder also suffers from a problem that an operator has to perform manual operations for changing the die plates because the extruder is not equipped with a unit for changing die plates.